1. Field of Invention
The invention relates to the technical field of a surface-modified composite solid particle and a method for producing the same.
2. Description of Related Art
There has so far been known in, for example, U.S. Pat. No. 4,915,987, a production process for a composite solid particle for the purposes of preventing coagulation, discoloration and deterioration and elevating dispersibility, catalytic effect and magnetic characteristics by fixing fine particles (hereinafter referred to as fine particles) on the surface of another particle which becomes a core (hereinafter referred to as a core particle). It has become possible to efficiently produce a functional composite or hybrid powder material (composite or hybrid powder) which is homogeneous and has stable characteristics by employing a high velocity gas stream impact method which is a dry particle compositing method requiring no organic solvent and no water, which is described therein.
However, in the composite solid particle produced by the method described above, the fine particles are merely stuck evenly on the surface of the core particle, and therefore a rough weight proportion of the fine particles exerting influence on an improvement in the functionality to the core particle depends on the surface area of the core particle and the cross section (projected area) of the fine particle. In general, it is considered that the maximum weight proportion of the fine particles to the core particle is a proportion in which the fine particles cover the surface of the core particle only in roughly one layer. Thus, the maximum weight proportion of the fine particles to the core particle is calculated from:
maximum weight proportion=(4rp1/Rp0)xc3x97100%
where:
r=radius of the fine particle
R=radius of the core particle
p1=density of the fine particle
p0=density of the core particle
As a result thereof, if the radii and the densities of the core particle and the fine particles are fixed, the maximum weight proportion of the fine particles is settled, and the weight proportion exceeding this cannot be achieved, which brings about the problem that little further elevation in the function can be expected. Thus, the problem to be solved by the invention is addressed to this point.
An object of the invention is to solve the problems discussed above.
The invention relates to a method for producing a composite solid particle by fixing fine particles on the surface of a core particle firmly in a non-peelable state, wherein the fine particles are embedded on the surface of the core particle, and then crystal of a fine particle component is allowed to grow on the above fixed fine particle-core particle composite.
The invention also relates to a composite solid particle obtained by modifying the surface of a solid particle by fixing fine particles on the surface of the core particle firmly in a non-peelable state, wherein crystal of a fine particle component is allowed to grow on the fixed particle-core particle composite.
In this regard, the fixed fine particle-core particle composite is mixed in a fine particle component solution to allow the crystal of the fine particle component to grow with the fixed fine particles described above being used as crystal nuclei. The fine particle component solution described above is produced by causing the fine particle component to react in a liquid phase. The fine particle component described above is calcium monohydrogenphosphate.
In this case, the crystal of the fine particle component is allowed to grow in an aqueous solution in which a hydrogen ion exponent (pH value) is adjusted to a range of 4 and 6, preferably between 4.5 and 5.8 and more preferably to 5.7.
Calcium monohydrogenphosphate is generated by adding pyrophosphoric acid to a suspension of calcium hydroxide and allowing them to react.
In the particle obtained by allowing the crystal to grow by carrying out the process of the invention, the content of the fine particles can be adjusted by the degree of the crystal growth, and therefore control can be carried out so that the content of the fine particles is freely increased, which has so far been found to be impossible using a conventional fixing method.
When the crystal grows long, as is the case with needle-like and columnar crystals, the surface area of the fine particle can notably be expanded.
Further, there can be obtained, as well, a composite solid particle in which needle-like and columnar crystals are connected to a core particle at a longitudinal end, which has so far been unobtainable using a conventional fixing method.
As the results described above, the composite solid particle obtained by allowing the fine particle component to grow to crystal not only can improve and elevate various functions (for example, electronic and magnetic characteristics, optical characteristics, thermal characteristics and biological characteristics) held by the fine particle to a large extent, but can also raise the compression moldability and the content-uniformizing characteristics. Further, a rise in the surface area of the fine particle can elevate various reaction rates.
The composite solid particle can be used for electric and electronic materials, magnetic materials, optical functional materials, medicines, cosmetics, biological materials and construction materials.